The present invention relates to a self-monitoring reflection light barrier with a measuring light emitter that emits light into a space to be monitored, and with a measuring light receiver which receives light reflected from an object disposed in the space to be monitored.
Reflection light barriers of the aforementioned type which are also designated as light sensors, are used, for example, for the recognition of objects, the monitoring of spaces, as collision protection for self-propelling vehicles, etc.
However, the prior art reflection light barriers and light sensors entail the disadvantage that a failure of the light barrier or light sensor cannot be readily distinguished from the normal operating condition because both during the failure of the light sensor as also when no object is being recognized, no signal occurs.
The present invention is therefore concerned with the task to so further develop a reflection light barrier (light sensor) with a measuring light emitter and a measuring light receiver of the type described above that a failure can be recognized with certainty.
The underlying problems are solved according to the present invention in that a further light receiver is provided which receives the light of the measuring light emitter without reflection and at least one further light emitter is provided which emits light in a test cycle which is received by the measuring light receiver without reflection.
According to the present invention, a further light receiver and a further light emitter are thus provided. The further light emitter receives the light of the measuring light emitter without the need that the light has to be reflected at an object. It is thus possible on the basis of the output signal of the further light receiver to examine whether the measuring light emitter emits light.
The further light emitter emits light in a test cycle which is being received by the measuring light receiver without reflection. It is possible by this test cycle to examine the measuring light receiver for a completely satisfactory functioning, i.e., it can be recognized whether it produces with an impinging light a corresponding output signal.
According to another feature of the present invention, a beam splitter plate is used which deflects the light of the measuring light emitter into the space to be monitored and which reflects the light reflected from the monitored space onto the measuring light receiver. "Behind" the beam splitter plate the further light emitter and the further light receiver are so arranged that they receive the light of the measuring light emitter passing through the beam splitter plate, respectively, the measuring light receiver receives the light of the further light emitter passing through the beam splitter plate. This arrangement offers a number of advantages:
On the one hand, it permits the construction of a compact reflection light barrier. On the other, it enables--as will be explained more fully hereinafter--a self-test function of the reflection light barrier which permits not only a recognition of a failure but additionally also an error coordination.
For example, with an arrangement in which the measuring light emitter and the measuring light receiver are arranged in front of the beam splitter plate adjacent one another in such a manner that the beam splitter plate deflects the light emitted from the measuring light emitter into the space to be monitored, respectively, deflects the light coming from the space to be measured onto the measuring light receiver, it becomes possible to provide a third light receiver which receives the light of the further light emitter reflected from the back side of the beam splitter plate. With an appropriate geometric construction, this light receiver can also additionally receive the light reflected from an object and therewith enables a further monitoring of the light receiver.
It is particularly advantageous in every case if the reflection light barrier according to the present invention includes an electronic control circuit which permits not only a read-out of the output signals of the measuring light receiver but which therebeyond can also carry out a self-test.
It is thereby particularly advantageous if the electronic control circuit, in addition to the measuring cycle, properly speaking, carries out a self-test cycle during which the function of the measuring light emitter and the function of the measuring light receiver are examined, as well as a so-called dark test, during which is examined whether outside light impinges on the individual receivers.